1. Field of the Invention
This invention relates to an image forming apparatus as an electrophotographic printer for printing an image using dry developer.
2. Description of Related Art
Such a conventional image forming apparatus typically forms an image through processes of charging a surface of its photosensitive drum uniformly, exposing the surface of the photosensitive drum to light for writing in order to form an electrostatic latent image, forming a toner image by clinging toner onto the electrostatic latent image, transferring the toner image to a transfer material such as a printing paper, fixing the transferred toner image onto the transfer material, and cleaning for eliminating the remaining toner, not transferred to the transfer material during the transferring process, from the surface of the photosensitive drum. There has been known an example in which a discharging process is provided for preventing the surface of the photosensitive drum from being formed with a remanent image after the transferring process before the charging process.
During the cleaning process of the conventional electrophotographic process described above, an elastic rubber blade is pushed to contact with the photosensitive drum to scratch and collect the remaining toner on the surface of the photosensitive drum mechanically. The toner collected during the cleaning process is stored in a waste toner container located within an electric photoconductor cartridge (hereinafter called "EP cartridge"), and is disused at the same time that the EP cartridge is exchanged after serving its time.
However, in this case, it is difficult to make the EP cartridge compact since the EP cartridge has to store the collected toner in the waste toner container located within the EP cartridge. Additionally, it is not preferable in terms of environmental protection since the collected toner will be discarded.
In another image forming apparatus, therefore, the toner remaining on the photosensitive drum is collected by a developing device itself, for instance, by a developing roller in the developing device, in lieu of the cleaning device, and the toner thus collected is reused.
However, the image forming apparatus in which the toner is collected by the developing roller composing the developing device to be reused, does not collect the toner adequately in the case that the remaining toner remains much on the photosensitive drum due to an insufficient transfer, and a positive remanent image occurs on the transfer material as stains. This is because during the developing process after the processes of charging and exposing, the apparatus collects the toner remained during the transferring process on the photosensitive drum.
When a light source such as a laser, an LED (Light Emitting Diode) array, or the like exposes the surface of the photosensitive drum serving with the remaining toner, the surface of the photosensitive drum, even if the surface should be exposed, is exposed inadequately by a photo-shielding effect caused by particles of the remaining toner on the surface of the photosensitive drum, so that a necessary electrostatic latent image may not be formed. In such a case, since an adequate or perfect electrostatic latent image is not formed due to shortage of the exposure, the toner does not adhere adequately to the photosensitive drum during the developing process, and a negative remanent image occurs due to shortage of density of the toner.